The present invention relates to free cutting alloy excellent in machinability.
Alloy has widespread applications because of a variety of characteristics thereof. A free cutting alloy excellent in machinability is, in a case, selected for improvement of productivity. In order to improve machinability, for example, free cutting alloy containing an element improving machinability such as S, Pb, Se or Bi (hereinafter referred to as machinability-improving element) is widely used. Especially in a case where machinability is particularly required because of precise finishing in machining or for other reasons, not only is a content of such a machinability-improving element increased in an alloy, but the elements are also added to an alloy in combination.
While S, which has widely been used for improvement of machinability, is in many cases added in the form of MnS, addition thereof in an alloy in a large content is causes for degrading corrosion resistivity, hot workability and cold workability of the alloy. Moreover, when the alloy is exposed to the air, a sulfur component included in the alloy is released into the air in the form of a sulfur containing gas, which causes sulfur contamination in peripheral areas of parts with ease. Therefore, there arises a necessity of suppressing release of sulfur containing gas (hereinafter referred to as improvement on out-gas resistivity). Elements such as S. Se and Te, however, deteriorate magnetic properties to a great extent in an electromagnetic stainless steel and the like.
Therefore, various proposals have been made: a Mn content is limited, a Cr content in sulfide is increased or in a case where S is contained, Ti is added in combination with S in order to disperse sulfide in the shape of a sphere (for example, see JP-A-98-46292 or JP-A-81-16653). To increase a Cr content in sulfide, however, tends to greatly decrease in machinability and hot workability and therefore, such an alloy has been restricted on its application in many cases.
Although such prior arts as JP11-140597 ('597), JP10-130794 ('794), JP2-170948 ('948), JP63-93843 ('843), JP60-155653 ('653) and U.S. Pat. No. 4,969,963 (Honkura et al.) disclose various free cutting alloys, these alloys are not satisfactory in machinability, sulfur out-gassing characteristics and elimination of Pb content.
It is accordingly an object of the present invention is to provide free cutting alloy excellent in machinability, showing outstanding characteristics as an alloy such as corrosion resistivity, hot workability and cold workability or specific magnetic characteristics, which are comparable to those of conventional alloys.